Rendering camera to image (ImageRender) not working
All I needed to do in your blend file was put the viewport in textured mode, then it started working. Other things you may like to consider:


It takes one frame for things to start happening, and because you're printing so many values, you have to wait a while.
the .valid attribute doesn't seem to work for ImageRender (it does for ImageFFMPEG though).
480*480*4 is nearly a million values. So if it looks like you're always getting 0's or 0xff's, you may not be. Try with a smaller image so you can see more of the data values
Consider unwrapping the plane and assigning it a shadeless texture so you can preview what is being displayed (you'll have to run texture.resresh(True) for it to update the texture instead of the buffer).
Consider switching to GLSL mode